An important aspect in the fields of medical diagnostics and biomedical research involves detection, identification, quantification, and characterization of various cells and biomolecules of interest through testing of biological samples such as blood, spinal fluid, cell culture and urine. Healthcare providers and biomedical researchers routinely analyze such biological samples for the microscopic presence and concentrations of cells and biomolecules.
For example, there is a need for validating the number of leukocytes (i.e. white blood cells) in a patient blood sample for blood transfusion qualification. By using an imaging cytometry method (Cellometer, Nexcelom Bioscience, LLC), leukocyte cell count can be measured by imaging a large area of a thin chamber, which allows counting of all the leukocytes within a specific scanned volume. Whole blood contains a high concentration of red blood cells, which often prevent the leukocytes from being seen by naked eyes, unless the red blood cells are lysed or a fluorescence method is used that specifically stains the leukocytes. With the detection methods mentioned above, the leukoreduction qualifying personnel would be able to focus on the leukocytes either using fluorescence or bright-field when red blood cells are lysed. However, most of the leukoreduced patient blood samples contain very low concentration of leukocytes; therefore, an imaging system may not be able to detect any presence of leukocytes, which means there is no object to focus on in the image field.
Therefore, a long-felt need exists for systems and methods that provide simple and accurate calibration and internal references for focusing and quality control so as to allow accurate and rapid imaging and measurement of ultralow concentration samples.